Seemed counter-intuitive & baffling, but someone in the office explained it to me better than that video.
Here's how he explained:
Let's suppose there are not 3, but 100 doors to pick from.
1 door contains car, remaining contain goats.
Initial choice:
P(me picking a goat, or wrong choice) = 99/100
Now, Monty blows 98 doors with goats (removes 98 wrong choices).
He does this because according to the rules of the game he MUST remove/eliminate the goats (wrong choices).
Hence, he now offers me the BEST possible choice.
So ask yourself - which choice is better:
- My initial choice of picking 99/100 goat (wrong choices)
Or, the BEST 1 of 99 he offers me now?
The answer is simple - his new offer is better than my old choice.